In a steering apparatus in which a telescopic position of a steering wheel or both a telescopic position and a tilt position of the steering wheel can be adjusted, after the telescopic position or both the telescopic position and the tilt position of the steering wheel are adjusted, an upper column needs to be clamped strongly and rigidly on to a vehicle body mounting bracket in such a manner as not to move from the clamped position. In view of this, a clamp device utilizing a single or a plurality of friction plates is provided for increasing the friction force used when the upper column is clamped, so as to clamp strongly and rigidly the upper column on to the vehicle body mounting bracket.
As a steering apparatus which includes a clamp device utilizing friction plates as described above, there is a steering apparatus described in Japanese Patent Unexamined Publication No. JP-A-10-35511. As is described in JP-A-10-35511, telescopic friction plates for clamping an upper column on to a vehicle body mounting bracket in a desired telescopic position are disposed on the upper column side which moves telescopically.
When the adjustment of the telescopic position is completed and the upper column is clamped on to the vehicle body mounting bracket, the upper column can be clamped strongly and rigidly on to the vehicle body mounting bracket by means of a frictional force produced by the telescopic friction plates when the upper column is so clamped.
However, the upper column fits on a lower column disposed towards a vehicular front side in such a manner as to move telescopically relative to the lower column so disposed. In order to realize a smooth telescopic movement of the upper column, a slight sliding gap is necessary in a fitting portion between the upper column and the lower column.
Consequently, even though the upper column is clamped strongly and rigidly on to the vehicle body mounting bracket, it has been inevitable that the rigidity and vibration properties of the steering apparatus as a whole are decreased due to the existence of the sliding gap in the fitting portion between the upper column and the lower column.
In order to increase the rigidity and vibration properties of the steering apparatus as a whole, the external dimensions and thicknesses of parts such as the upper column, the lower column and the vehicle body mounting bracket are increased, but this causes a problem that costs for parts as well as the weight of the steering apparatus and hence of the vehicle are increased.